1. Field of the Invention
The present invention relates to monohulls with stern stabilizers for high-speed ships.
The technical field of the invention is that of ship building, and more particularly manufacturing ship hulls.
2. Description of the Related Art
The main application of the invention is building high-speed ships, i.e. capable of more than 38 knots or as much as 54 knots or even more, of mean length greater than 50 meters (m), and capable of carrying in particular passengers and vehicles both for civilian and for naval uses.
Over thousands of years, boat building has made considerable progress in ship propulsion for increasing speed and endurance: starting from muscle power in the time of the ancient Egyptians to wind power, and then to steam and oil and recently atomic energy. However during this revolution in terms of drive, hulls have hardly changed at all: monohulls have always been favored because of simplicity, light weight, and buoyancy, both static and dynamic, even though stability, at least in terms of comfort, is not perfect.
However, over the last few years, numerous novel designs have been studied and developed to take the place of the monohull with the purpose of achieving greater speed and better stability, with this being at the request both of navies and of shipping companies; shipping companies would like to become much more competitive than airlines by seeking to reduce the time required to cross an ocean to half or less while being capable of carrying many more passengers than can be carried by a large airliner. Nevertheless, it is clear that many very large vessels are probably going to remain monohulls for a long time yet, particularly in circumstances where neither stability nor high speed are considered as being major advantages, such as in transporting oil, for example.
To achieve high speeds, i.e. speeds greater than 30 knots, various types of hull have been developed, some making use solely of hydrostatic support like monohulls but by increasing the number of hulls, as with catamarans and trimarans in particular; hydrodynamic support has also been used by means of underwater "wings" which serve to lift the load-carrying hull out of the water above a certain speed; other principles have been developed, in particular those using aerostatic support, such as air cushion vehicles.
The present invention makes use of all of those support principles on the basis of a trimaran type design; until now, development and implementations of three-hulled ships have been associated essentially with recreational boating and in particular with sailing, specifically for the purpose of beating speed records: however, in that type of use, the float situated upwind from the central hull is functionally practically unused, the boat then being supported by the central float and by the side float on the downwind side. Various trimaran hull designs have also been developed to beat mechanical propulsion speed records, but without seeking to carry goods or passengers, for example the ship described in Australian patent application AU 521518: that relates to a kind of trimaran having three hydroskis enabling it to travel on three support surfaces disposed in a triangular configuration, one at the bow and the other two at the stern, and enabling the hull to be lifted completely out of the water, but that cannot be extrapolated to a heavy transport ship for carrying passengers or vehicles.
In the field of commercial transport, rather few projects have been developed. French published patent applications FR 2671775 and FR 2675460, corresponding to U.S. Pat. No. 5,529,009, describe multi-hull ships, none of which have been built at this time, doubtless because of problems relating essentially to stability and cost. These publications relate to hulls in which the superstructures and the central float are rather conventional, even though the side floats are quite fine, but incapable of achieving maximum speeds in excess of 40 knots. In addition, the hulls are rather heavy and the usable portions of their superstructures and their overall centers of gravity are placed very high above the water.
In any event, at present and without profligate use of power for propulsion purposes which then makes the ship uncomfortable because of vibration and which is not economically feasible, no high-speed ship can travel faster than 35 knots under normal circumstances because the ship is limited by hydrodynamic resistance to forward travel which increases with the cube of speed, specifically for high speeds in excess of 30 to 35 knots.
The problem posed is thus to be able to make ships capable of transporting passengers and/or freight, such as vehicles for the most part, that is at least 50 m long, that is suitable for traveling at high speed in excess of 40 knots and even of 50 to 60 knots, whatever the weather conditions, while maintaining acceptable stability in terms of rolling and pitching, firstly to make it comfortable to travel in, in particular for passengers, and secondly to avoid overstressing the structures of the hulls which must be simple to manufacture, rigid, and strong.